Despite anecdotal evidence of changes to tennis ball characteristics and play properties, little research has
been directed towards understanding the causes and effects of tennis ball degradation. Improved racket
technology and player fitness have contributed to an increase in the speed of the game, yet balls have
seen few advancements over the same period. There are several obvious factors contributing to tennis ball
degradation: natural pressure loss in pressurised balls, changes to the cloth covering due to court and
racket impacts, and precipitation and environmental factors. As recent tennis research has focused on the
properties of new balls, there is a need to investigate other ball conditions present in the game of tennis.
This thesis provides a structured investigation into the causes and effects of ball degradation, an objective
assessment of the effects of degradation on ball performance, and incorporates subjective perceptions of
ball aesthetics and play properties noted by players. Particular attention is given to ball fuzziness. Excessive
fuzziness can occur from manufacturing variability, court and racket interactions, and environmental
conditions - though there is currently no standardised method to assess ball surface condition.
An objective measure of ball fuzziness has been developed and used in the analysis of nearly 4000
individual ball images. The effects of court and racket impacts, precipitation, natural pressure loss, and
repeated impacts have been analysed for their effects on ball degradation. An assessment of ball performance
utilised ball impact and aerodynamic data to determine significant differences between balls and
develop an improved ball trajectory model.
Several player perception investigations were conducted using professional, elite, and standard club
players. Two internet based investigations incorporated aspects of sensory evaluation studies to produce
new techniques in evaluating products for the sports industry. An investigation into ball aesthetics was
used to determine the relative importance of ball attributes on ball playability and important areas of
perceived ball feel and performance were assessed during testing with elite players. Significant differences
in perception were then combined with objective data to establish perceptible thresholds of wear and
degradation in tennis balls and significant areas in player perception. This thesis presents a large body of work on tennis ball degradation. Results provide a mechanism
to structure future investigations, new analysis techniques, and objective and subjective analyses of ball
degradation. The developed digital fuzziness metric shows good agreement with player perception and
aerodynamic data and provides a method to objectively compare ball conditions. Naturally aged and
fuzzy balls produced the most noticeable differences in ball impact properties, though the aerodynamic
data used in the development of an improved trajectory model suggests that ball spin could play a more
significant role in ball flight than drag force differences.
Subjective assessments of ball appearance suggest ball fuzziness is nearly twice as important as the
condition of the ball's logo in determining ball playability. Player testing indicated inconsistent responses
and limited differentiation in the perceived feel and performance properties of naturally aged balls. The
visible differences in the fuzzy balls improved player responses, indicating the importance of aesthetics in
perceived ball properties. Flight speed, hardness, liveliness, bounce speed, and bounce height are areas of
perceived ball feel and performance that show good agreement with measured ball properties and usefulness
in future work.
Directions for future work include developing a ball performance model, expanding the digital fuzziness
metric to produce an overall measure of ball degradation, and further laboratory and perception testing.

Description:

A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.